The present disclosure relates to a plurality of printing or image recording apparatuses providing a multifunctional and expandable printing system. It finds particular application in conjunction with integrated printing modules consisting of several marking engines, each having the same or different printing capabilities, and will be described with particular reference thereto. However, it is to be appreciated that the present disclosure is also amenable to other like applications.
Various apparatuses for recording images on sheets have heretofore been put into practical use. For example, there are copying apparatuses of the type in which the images of originals are recorded on sheets through a photosensitive medium or the like, and printers in which image information transformed into an electrical signal is reproduced as an image on a sheet by an impact system (the type system, the wire dot system or the like) or a non-impact system (the thermosensitive system, the ink jet system, the laser beam system or the like).
The marking engine of an electronic reprographic printing system is frequently an electrophotographic printing machine. In such a machine, a photoconductive belt is charged to a substantially uniform potential to sensitize the belt surface. The charged portion of the belt is thereafter selectively exposed. Exposure of the charged photoconductive belt or member dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image on the photoconductive member is subsequently transferred to a copy sheet. The copy sheet is heated to permanently affix the toner image thereto in image configuration.
Multi-color electrophotographic printing is substantially identical to the foregoing process of monochrome printing. However, rather than forming a single latent image on the photoconductive surface, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complementary thereto. This process is repeated a plurality of cycles for differently colored images and their respective complementarily colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multi-layered toner image on the copy sheet. Thereafter, the multi-layered toner image is permanently affixed to the copy sheet creating a color copy. The developer material may be a liquid or a powder material.
In the process of monochrome printing, the copy sheet is advanced from an input tray to a path internal to the electrophotographic printing machine where a toner image is transferred thereto and then to an output catch tray for subsequent removal therefrom by the machine operator. In the process of multi-color printing, the copy sheet moves from an input tray through a recirculating path internal the printing machine where a plurality of toner images is transferred thereto and then to an output catch tray for subsequent removal. With regard to multi-color printing, as one example, a sheet gripper secured to a transport receives the copy sheet and transports it in a recirculating path enabling the plurality of different color images to be transferred thereto. The sheet gripper grips one edge of the copy sheet and moves the sheet in a recirculating path so that accurate multi-pass color registration is achieved. In this way, magenta, cyan, yellow, and black toner images are transferred to the copy sheet in registration with one another.
Additionally, it is common practice to record images not only on one surface of the sheet, but also on both surfaces of a sheet. Copying or printing on both sides of a sheet decreases the number of sheets used from the viewpoint of saving of resources or filing space. In this regard as well, a system has been put into practical use whereby sheets having images recorded on a first surface thereof are once accumulated and after the recording on the first surface is completed, the accumulated sheets are then fed and images are recorded on a second surface thereof. However, this system is efficient when many sheets having a record of the same content are to be prepared, but is very inefficient when many sheets having different records on both surfaces thereof are to be prepared. That is, when pages 1, 2, 3, 4, . . .are to be prepared, odd pages, i.e. pages 1, 3, 5, . . .must first be recorded on the first surface of the respective sheets, and then these sheets must be fed again and even pages 2, 4, 6, . . .must be recorded on the second surface of the respective sheets. If, during the second feeding, multiplex feeding or jam of sheets should occur, the combination of the front and back pages may become mixed, thereby necessitating recording be done over again from the beginning. To avoid this, recording may be effected on each sheet in such a manner that the front and back surfaces of each sheet provide the front and back pages, respectively, but this takes time for the refeeding of sheets and the efficiency is reduced. Also, in the prior art methods, the conveyance route of sheets has been complicated and further, the conveyance route has unavoidably involved the step of reversing sheets, and this has led to extremely low reliability of sheet conveyance.
Also, there exist further requirements to record two types of information on one surface of a sheet in superposed relationship. Particularly, recently, coloring has advanced in various fields and there is also a desire to mix, for example, color print with monochrome print on one surface of a sheet. As a simple method for effecting a superposed relationship, there exists systems whereby recording is once effected in monochrome, whereafter the developing device in the apparatus is changed from a monochrome one to a color one, and recording is again effected on the same surface. This system requires an increase in time and labor.
Where two types of information are to be recorded on one surface of the same sheet in superposed relationship, sufficient care must be taken of the image position accuracy, otherwise the resultant copy may become very unsightly due to image misregistration or deviation from a predetermined image recording frame.
In recent years, the demand for even higher productivity and speed has been required of these image recording apparatuses. However, the respective systems have their own speed limits and if an attempt is made to provide higher speeds, numerous problems will occur and/or larger and more bulky apparatuses must be used to meet the higher speed demands. The larger and bulkier apparatuses, i.e. high speed printers, typically represent a very expensive and uneconomical apparatus. The expense of these apparatuses along with their inherent complexity can only be justified by the small percentage of extremely high volume printing customers.